1. Field of the Invention
The present invention relates to a process for manufacturing minute capsules, en masse, in a liquid manufacturing vehicle. More particularly, the process of the invention involves liquid-liquid phase separation of a relatively concentrated solution of polymeric material to be used in the formation of walls for the minute capsules.
En masse processes for the manufacture of microcapsules have generally required large amounts of liquid manufacturing vehicle and have generally resulted in low yields of capsules. An encapsulating system and process which utilizes relatively small amounts of manufacturing vehicle to generate relatively large amounts of microcapsules would be valuable from several viewpoints. For example, the costs of transporting the capsule product, as manufactured, would be reduced because the product contains less vehicle. As another example, in the case where the capsule product is to be coated to a dried film on a sheet substrate, coating costs are reduced because there is less liquid vehicle to be removed from the substrate.
Many combinations of materials have been used in the past in search of compositions which yield certain physical characteristics in capsule walls or which permit performing the encapsulating process under certain desired or required conditions. As examples of desirable capsule characteristics, small size, impermeability of capsule walls to diffusion and the strength of capsule walls to withstand normal handling forces can be mentioned. As examples of desirable process conditions, relatively high pH, relatively short times, and relatively high yields and concentration are important.
It is, therefore, an object of the present invention to provide a capsule manufacturing process wherein capsules are produced in high yield, in high concentration and over a wide range of operable reaction temperatures.
Another object of the invention is to provide a process which requires a relatively shorter time for completion and which utilizes process conditions of increased convenience.
A further object of the present invention is to provide a process for manufacturing microcapsules, which microcapsules have walls of increased resistance to accidental rupture.
It is yet another object of this invention to provide a process for producing microcapsules which have little color when containing basic chromogenic materials.
It is a specific object of this invention to provide an encapsulating process wherein the capsule wall material comprises a melamine-formaldehyde polymeric material wherein the melamine-formaldehyde wall material is generated by an in situ condensation reaction in the presence of a negatively-charged, carboxyl-substituted, linear aliphatic hydrocarbon polyelectrolyte material dissolved in the capsule manufacturing vehicle.
These and other objects and advantages of the present inventio will become more apparent to those skilled in the art from a consideration of the following specification and claims.